Bearing piles must be driven into the ground for a distance sufficient to provide a load bearing capacity that is determined by the weight of the structure which is supported by the piles. This does not pose problems in instances where rock is present close to the surface of the ground. A pile is simply driven firmly into the rock. One or a combination of two other techniques have traditionally been used in instances where rock lies deep below the surface of the ground.
A first such technique, termed friction bearing, relies on the progressive increase in frictional resistance to further penetration that occurs as a pile is driven progressively further into the ground. This resistance can be determined by measuring the penetration which occurs in response to each pile driver blow and at some point becomes sufficient to support the load which the pile is to bear. The other technique, termed end bearing, involve driving the pile through unconsolidated surface material until sufficiently stiff, consolidated or hard material is encountered to provide the desired load bearing capacity by soil pressure against the base of the pile.
Either of the above described techniques usually requires a very lengthy penetration of the pile into the ground. It would be advantageous to reduce the costs of pile material and pile driving time by enabling adequate load bearing capacity at shallower depths of penetration.
Various methods have used to achieve this goal by enlarging the end bearing area of the pile with a body of concrete. This may, for example, involve excavation of a sizable cavity at the base of the pile within a bell caisson or forming of a rammed concrete pile by hammering fresh concrete down a tubular pile casing. In some instances a cavity for receiving the concrete has been formed by detonating an explosive at the base of the pile. All of these methods require costly specialized equipment and material, are time consuming and can be dangerous to persons involved in installation of the pile. In addition the load bearing capacity of these installations is speculative since no dynamic loading occurs after the enlargement.
The present invention is directed to overcoming one or more of the problems discussed above.